Piston ring seals are generally seated in a groove formed in the outer circumference of a piston and perform at least two functions to ensure efficient operation of the engine. First, during the power cycle, the ring seals prevent gases under high pressure from bypassing the piston. Thus, maximum driving force is applied to the piston. Second, on the return stroke, the ring seals prevent lubricants from entering the combustion chamber. If the ring seals fail to perform efficiently, the engine will not develop the maximum power due to “blow-by” on the power cycle. Additionally, if the ring seals leak during the return stroke, lubricants will enter the combustion chamber, thereby reducing combustion efficiency and increasing air pollution by way of the exhaust cycle. Generally, the ring seal provides the interface between the piston and the cylinder wall. Accordingly, the general configuration of the ring seal at least partially determines the friction between the piston assembly and the surfaces of the engine bore during operation. Further, this frictional characteristic influences efficiency of the engine, such that reduced friction generally leads to increased fuel economy.
One known piston ring design includes two separate piston rings that contact the engine bore surface to provide a seal. While the provision of two piston rings allows for enhanced sealing against the bore surface, the use of two separate rings also necessarily increases the amount of friction against the bore surface.
Accordingly, there is a need for a piston ring design that provides reduced friction between the piston assembly and the engine bore surfaces while maintaining an adequate seal between the piston and the bore surfaces.